1. Field of the Invention
The present invention relates to medicine and more particularly to the use of electrodes applied to the skin of the patient in electroconvulsive therapy (ECT).
2. Description of the Related Art
Electroconvulsive therapy ("ECT"), sometimes called "shock therapy", is used to treat major depression. A report of a NIMH panel (National Institute of Mental Health), reported in Science (June 28, 1985, pg. 1510, 1511), concluded that "not a single controlled study has shown another form of treatment to be superior to ECT in the short-term management of severe depressions." The Science article noted that the complication rate is about 1 in 1700 treatments and severe and prolonged memory loss is extremely rare, and possibly non-existent.
In an ECT treatment, two electrodes are applied to the skin of the patient, at the head, and a small electric current passes through the electrodes. Only a small portion of the current reaches the brain as the rest is deflected by the skin and skull. The current excites neural tissue, triggering a seizure which resembles, on an EEG display (electroencephalograph) the seizures of epilepsy.
In the "Thymatron" ECT instrument (TM of Somatics, Inc., Lake Bluff, Ill.), the stimulus is a brief series of electrical square waves. The stimulus is a constant current of 0.9 amps limited to 450 volts, consisting of 140 bipolar pulses per second of 1 msec. width, which is adjustable 0.2-4.0 seconds in duration.
At the present time, the electrodes that are used in ECT are flat or concave metal disks that are reusable. The metal disk, if simply held on the skin, would present too great an electrical impedance. The skin may be, for example, the skin of the scalp or forehead. The impedance is reduced to an acceptable level by using a conductive gel or a conductive saline (salt) solution pad.
However, both the gel and the saline pad present serious problems.
The gel used is a thick, viscous conductive aqueous gel. The metal disk electrodes are covered with the thick gel. The electrodes are held on the skin of the patient by pressure from a perforated rubber headstrap or from electrically insulated handles held by a therapist. The viscous gel remains on the skin after the metal electrodes are removed and the gel should then be removed. However, sometimes the gel is not fully removed from the skin, scalp, or hair after the ECT treatment. The crusted gel residue may compromise the confidentiality of the ECT treatment, and some patients find its presence aesthetically displeasing.
As an alternative to conductive gel, disk electrodes are sometimes covered with saline (salt) soaked pads to reduce the skinelectrode electrical impedance. However, the saline eventually corrodes the metal electrodes and their wire leads, reducing and ultimately blocking the electrical stimulus. The failure of the electrodes, due to corrosion, is unpredictable as the corrosion may be hidden. Any excess of saline that leaks out of the pads may create an electrical short circuit between the electrodes. Such short circuits may not be noticed and yet may prevent delivery of the full electrical stimulus to the patient's brain.
The use of gel or saline solution, with metal electrode disks, presents other disadvantages. First, frequently the metal disk electrodes, whether flat or concave, fail to closely conform to the anatomical topography of the region of the patient's head. The patient's head may be more curved, or less curved, than the face of the electrode. Such incomplete contact reduces the contact area and increases the possibility of slippage and skin burn. Secondly, therapists, and anesthetists who administer ECT, repeatedly come in contact with the patient's head during treatment. They may accidentally touch the conductive surfaces of the electrode disks, receiving an electrical shock, which is painful and may be dangerous, for example, if the shock crosses the heart. Thirdly, the disks must be carefully washed between uses, to remove the gel or saline residue and prevent contamination, and possible infection, of one patient by another. Fourthly, the disk electrodes are subject to corrosion from incompletely removed gel or saline solution, and they may be damaged if dropped or mishandled.
Often the disk electrodes are held to the patient's head by an elastic headband. Some patients object to the sensation of continuous pressure on their temples when a rubber headband (headstrap), with metal electrode assembly, is tightened on their head. Such headstraps, and electrode assemblies, are subject to breakage and loss.